Lifetime error when using nested views

[jafioti]

When using nested views and an action callback, a lifetime error is thrown.

Steps to reproduce the behavior:
Open any sycamore project and paste:

#[component]
pub fn TempComponent<G: Html>(ctx: Scope) -> View<G> {
    let action = |_| ctx.spawn_local(async move {});
    view!{ctx, 
        ({
            view!{ctx, 
                input (on:click=action)
            }
        })
    }
}

Expected that no lifetime error is thrown since this is valid code.

• Sycamore: master

[lukechu10]

This regression was introduced by 9fdff59 because it adds an addition create_effect_scoped call.

Unfortunately, this change is necessary to prevent memory leaks and it seems like it interferes with Rust's borrow checker. I suspect it has something to do with the invariance of the lifetime parameter on Scope because accessing a signal or other from inside the closure works.

In other words, the following works:

#[component]
pub fn TempComponent<G: Html>(ctx: Scope) -> View<G> {
    let action = |_| {
        ctx.create_signal(0);
    };
    view!{ ctx, 
        ({
            view!{ ctx, 
                input (on:click=action)
            }
        })
    }
}

I'm guessing because &'a Signal<i32> is covariant over 'a.

If somebody can figure this out, that would be greatly appreciated!

[lukechu10]

But for your specific use case, since the interpolated value is not actually reactive, you can just create the inner view outside of the outer view like so:

#[component]
pub fn TempComponent<G: Html>(ctx: Scope) -> View<G> {
    let action = |_| ctx.spawn_local(async move {});
    let inner = view!{ ctx, 
        input (on:click=action)
    };
    view!{ ctx, 
        (inner)
    }
}

[lukechu10]

Eureka! This is because of rustc non-lexical-lifetimes "migration mode". If you add #![feature(nll)] with nightly toolchain, the issue is fixed!

[lukechu10]

Rust tracking issue for turning off nll migration mode: rust-lang/rust#58781

[lukechu10]

Release v0.8 now relies on nll mode so I will close this issue. Please create a new issue if your problem is not resolved.